Various products including hard disk drives utilize a read channel device to retrieve information from a medium and decode and convert the information to a digital data format. Such read channel devices may include data processing circuits including encoder, detector and decoder circuits to encode, detect and decode data as it is stored and retrieved from a medium or transmitted through a data channel, in order to reduce the likelihood of errors in the retrieved data.
It is important that the read channel devices be able to rapidly and accurately detect the data bits in retrieved or received data samples so they can be decoded. A number of various types of detectors are available to identify the value of encoded data bits as they are retrieved or received, before the detected data is decoded. One such detector is a maximum a posteriori (MAP) detector, which determines the most likely value of each encoded data bit. A typical MAP detector uses a trellis structure to calculate the probability or branch metric for each possible value of a bit or group of bits. A forward pass through the trellis is performed, calculating the probabilities of the possible values, a backward pass through the trellis is performed, again calculating the probabilities of the possible values, and the results of the forward and backward passes are combined to arrive at a decision based on the probabilities.
Because efforts are continually being made to increase the speed of data processing circuits while reducing their size and complexity, all while operating with increasingly dense storage devices or transmission channels that increase noise, there exists a need in the art for improving data detection in data processing circuits.